I think it is anachronistic to use the term "anti-semitic" (with all its implications of Christian and later racial anti-semitism) for what could better be regarded as anti-Judean polemic. This better fits with the meaning of Ioudaioi in first-century Greek and the nature of Gentile prejudice against Jews (i.e. those strange people from that backward province). Yet there is here an ambiguity -- does Ioudaioi include those people in the diaspora who were of Judean descent or does it only include those who were citizens of Judea? From the point of view of most Gentiles, there wasn't a difference -- they were all Judeans if they followed the Judean way of life and/or were of Judean descent. From the point of view of diaspora Jews, one could view himself or herself as a Judean in this sense, or one could define oneself instead as an Israelite or of the "seed of Abraham", or one could define oneself as a Roman citizen (in the case of those who were free). Paul was not a Judean in the sense of being a citizen of Judea, and he is depicted in Acts 22:25-28 as strategically declaring himself as a Roman (Rhómaios) who was a citizen (politeian) by birth (gegennémai), whereas in Romans 1:11 he defines himself as an Israelite (egó Israelités eimi) rather than as a Judean. It is in terms of the binary contrast between Gentiles (those not of the circumcision) and those who were "Jews" (= Judeans) "by nature" (i.e. through descent and through circumcision) that Paul declares himself a "Jew". So in Galatians 2:15 he referred to himself and other Jewish Christians as "we Judeans by nature" (hémeis phusei Ioudaioi); he was not here defining Judeans as those who live in Judea.
With respect to the passage in 1 Thessalonians, it is worthwhile to observe two things. The use of the term Ioudaioi in v. 14 does indeed appear to refer to Judeans as those belonging to the province of Judea because (1) it follows the reference in the same verse to Christians who were living "in Judea" (en té Ioudaia), and (2) these Ioudaioi that caused suffering to those Christians "in Judea" are parallel to the "fellow countrymen" (idión sumphuleton) of the Christians in Thessalonika (humeis). This parallel would imply that the Ioudaioi are similarly fellow countrymen of the Christians living "in Judea". So I don't think the author is using the term here in an ethnic sense as in Galatians 2:15 and there isn't the kind of ethnic anti-semitism latent in later Christian citations of 1 Thessalonians 2:15 in subsequent anti-Jewish polemic (particularly in the meme of the Jews being "Christ killers", which has this verse as one point of departure). The reference is to persecution of Judean Christians at the hands of their own countrymen. But it is also significant to observe that the author's reference to the Judeans "who killed Jesus and the prophets" (apokteinantón Iésoun kai tous prophétas) is allusive of the inner-Jewish polemic in 1 Kings 19:10 (cited also in Romans 11:3) and Nehemiah 9:26-27, where the "sons of Israel" are described as having "killed your prophets" (tous prophetés sou apekteinan). In Deuteronomistic ideology, the nation as a whole is held guilty for the sins of those who killed the prophets (hence it was punished and went into exile at the hands of the Babylonians) and a similar idea is found in Jeremiah 26:15 in which the prophet says: "If you put me to death, you will bring the guilt of innocent blood on yourselves and on this city and on those who live in it". The handwashing ritual in Deuteronomy 21:6-8, intended to absolve the nation of the guilt of innocent blood ("Set not the guilt of innocent blood in the midst of your people Israel"), is utilized in the Matthean trial scene with Pontius Pilate (Matthew 27:24-25) to pin the guilt of executing an innocent man (Jesus) on the people of Jerusalem who declare: "His blood be upon us (to haima autou eph' hémas) and on our children". This scene is foreshadowed in Matthew 23:29-38, which refers to the city of Jerusalem as "you who kill the prophets (apokteinousa tous prophetés) and stone those sent to you" and the Pharisees as "the children of those who murdered the prophets (phoneusantón tous prophetés) ... upon you will come all the innocent blood (elthé eph' humas pan haima dikaion) shed on the earth", which would result in the coming destruction of Jerusalem and its temple (23:38-24:2). There is a very similar background and concept on the passage in 1 Thessalonians 2:14-16 and I believe it shares the same polemic. It is a traditional inner-Jewish polemic (molded on that found in the OT) that regards the city of Jerusalem and the nation of Judea as sharing guilt for the killing of Jesus and the persecution of the apostles, just as they previously shared in the same guilt in the killing of the OT prophets. There is a clear difference between this kind of polemic and later Christian polemic (in place already in the second century AD) that generalized this guilt to all ethnic Jews.
On the other hand, the statement in 1 Thessalonians 2:13 goes further than Matthew by resonating also with Gentile anti-Judean polemic. The statement that the Judeans "are hostile to all men" is paralleled by Tacitus' charge (in Historiae 5.5) that the Judeans "regard the rest of mankind with all the hatred of enemies" (adversus omnes alios hostile odium), and it is generally recognized this accusation was a commonplace among Gentiles (cf. Tacitus, Annals 15.44, Juvenal, Satyricon 14.103-104, Diodorus Siculus, Bibliotheca Historia 34-35.1.1-5, Josephus, Contra Apionem, 2.148, Antiquities 4.137-38, 8.117, 11.212, 13.245, 16.42), which represents a Gentile interpretation of Jewish ritual purity with respect to fellowship with non-Jews (see especially Josephus, Contra Apionem 2.258 regarding Jews "not wishing to share fellowship with those who choose to live according to a different way of life"). There is an interesting Christian reinterpretation of this charge however in 1 Thessalonians 2:15. The Judeans responsible for persecuting the Christians in Judea were interfering with the Christian mission to the Gentiles, thereby standing in the way of their salvation. They were "hostile to all men in their effort to keep us from speaking to the Gentiles so that they may be saved". In light of the resistance that Paul faced from Torah-observant Jewish-Christians (as reported in Galatians and Acts), particularly those affiliated with James the Just who pressed for circumcision and the maintenance of ritual separation from uncircumcised Gentile Christians, it appears that this passage in 1 Thessalonians has an inner-Christian polemic as well by treating these Jewish-Christians as simply "Judeans" and not those belonging to the "churches of Christ in Judea". The fact that this passage adapts a Gentile charge against Jews that specifically had ritual separation as its focus fits very well with the conflict that the Pauline churches faced with Jewish-Christians that insisted on ritual separation with uncircumcised Gentile Christians (cf. later Ebionite writings like the Ascents of James and the Epistula Petri which portrayed Paul as an "enemy" apostate from the Law).
Finally it is worth noting that some scholars regard 1 Thessalonians 2:13-16 as a deutero-Pauline interpolation into the text of 1 Thessalonians (cf. Pearson, HTR 1971 and Schmidt, JBL 1983). The evidence is not conclusive, but there are a number of suggestive clues: (1) The personal message from Paul about his last visit to Thessalonika in v. 17 picks up from his description of his visit in v. 11-12, with the section in v. 13-16 being a parenthetical digression, (2) the portion of the letter from 2:1 onward is the main body of the letter, following an opening thanksgiving in 1:2-10, but the section in v. 13-16 is an unexpected second thanksgiving that imitates the language and thought of the first thanksgiving in roughly the same order (eukharistoumen tó theó peri panton humon || hémeis eukharistoumen tó theó in 1:2, 2:13; adialeiptós || adialeiptós in 1:3, 2:13; ergou tés pisteós || energeitai ... tois pisteuousin 1:3, 2:13; euaggelion hémón en logó || logon theou in 1:5, 2:13; kathós aléthós || kathós oidate in 1:5, 2:13; dexamenoi ton logon || edekasthe logon in 1:6, 2:13; mimétai egenéthéte || mimétai egenéthéte in 1:6, 2:14; en thlipsei || hémas ekdióxantón in 1:6, 2:15; en té Makedonia kai Akhaia || en té Ioudaia in 1:8, 2:14; ekhein hémas lalein || kóluontón hémas ... lalésai in 1:8, 2:16, tés orgés tés erkhomenés || ephthasen hé orgé in 1:10, 2:16), with both thanksgivings ending in an eschatological climax with a reference to the coming "wrath" of God, (3) this second thanksgiving has marks of a non-Pauline syntax and style (e.g. kai as a connector of two main clauses being found nowhere else in 1 Thessalonians, the unusual position of vocative adelphoi in v. 14 between constituents of another noun phrase, the unique splitting up of "Lord Jesus" with a participle in v. 15, etc.), (4) although Paul elsewhere can have some rather strident rhetoric against his Jewish-Christian adversaries (Galatians 5:12 comes to mind, where Paul wishes that those insisting on circumcision for Gentiles would castrate themselves), he nowhere holds the Jews/Judeans/Judaizers responsible for the death of Jesus which he instead obliquely attributes to the "rulers of this age" in 1 Corinthians 2:8, (5) the eschatological climax in v. 16 appears to be allusive of several extracanonical writings (pros ekplérósin tón hamartión ... pros telos || eis to anaplérósai tas hamartias ... eis telos in 2 Maccabees 6:14-15, 1 Thessalonians 2:16; ephthasen de autous hé orgé tou theou eis telos || ephthasen de ep' autous hé orgé eis telos, Testament of Levi 6:11, 1 Thessalonians 2:16), and (6) the aorist ephthasen in v. 16 should be taken as alluding to an event that was already past and the phrase eis telos highlights the finality of this "wrath" against the Judeans which has already taken place. It is possible that the author has simply kept the aorist from its source in the Testament of Levi, but in its present context it may best be interpreted as referring to the destruction of Jerusalem in AD 70. The same recompense is specified in Matthew 23-24 for those who "killed the prophets," and as already mentioned there is a close similarity between the polemic found in Matthew and 1 Thessalonians 2:15-16. This is probably the strongest argument for the interpolation hypothesis, but the evidence supporting this proposal is imho less conclusive than in other suspected instances of interpolation in Paul.