Abstract: This paper studies whether college admission competitiveness affects the college field choice decision of students in a field-specific college admissions system. To do this we leverage a college admission policy reform in Ethiopia that exogenously increased the proportion of college seats allocated to pre-college STEM track students at expense of those in the Humanities track. Using detailed academic records of nearly 2 million students we compare the field choice behavior of cohorts before and after the reform. The reform resulted in a significant decrease in admission selectivity of college STEM fields in the short run. A reduced form estimate shows that students are significantly more likely to choose the pre-college STEM track after the reform and the increase is the largest among the marginal students. Using a complier analysis, we also show that the reform induced Roy (1951) type positive selection on field-specific skills. Specifically, the compliers have a comparative advantage in STEM-relevant skills while never-takers are relatively better in skills valued in Humanities. Finally, we estimate a counterfactual admission probability of the compliers and the never-takers. The estimates show that compliers gained close to 12 percentage points while the never-takers lost 6 percentage points in the probability of college admission. Overall, these results suggest that in a field-specific college admission system, admission uncertainty plays a critical role in the college field choice decisions of students.