This study attempted to test the threshold hypothesis in second/foreign language (L2) reading by investigating the relations among first language (L1) reading, L2 knowledge, and L2 reading comprehension in a sample of 2666 (1333 males and 1333 females) Korean EFL high school students. Three different methods of data analysis were utilized after closely looking into the methods of data analysis of the current literature on a language threshold. Statistical analysis revealed that the contribution of L1 reading and L2 knowledge to L2 reading was significant and substantial in the main and interaction effects, accounting for 54 percent of variance of L2 reading comprehension in tandem. However, the correlation of L1 reading to L2 reading showed, in general, a decreasing trend in accordance with the improvement of L2 knowledge, which is in contrast with the notion of a threshold level. This result of a language threshold was discussed in terms of a broad construct of language transfer and the interactive approach to reading in an L2.