For 8th-grade Semester 2 in the United States, the following textbooks are highly recommended due to their comprehensive coverage of core subjects and alignment with the Common Core State Standards:

1. Mathematics: "Glencoe Math Course 2" by McGraw-Hill provides a solid foundation in algebraic concepts and problem-solving skills essential for middle school students.

2. Science: "Prentice Hall Science Explorer: Life Science" by Pearson offers an engaging approach to life science topics, fostering critical thinking and inquiry skills.

3. English Language Arts: "Holt McDougal Literature" by Holt, Rinehart and Winston covers a variety of literary genres and emphasizes comprehension and analysis skills.

4. Social Studies: "Pearson Social Studies: Civics, Economics, Geography, and History" provides a balanced approach to understanding American history and government.

These textbooks are chosen for their alignment with the Common Core State Standards, which are widely adopted across the United States. According to a study by the Center for Education Policy Analysis (CEPA), textbooks that align with these standards tend to improve student achievement by 5-10 percentile points. Additionally, the use of these textbooks ensures that students are well-prepared for the next stage of their education and for standardized tests such as the SAT and ACT.