Many technology companies struggle to fill all their positions and to achieve gender parity in their ranks. One explanation for gender disparities is the possibility that men and women differ in their willingness to work under competitive organizational environments of tech firms. To investigate this question, this paper reports on a large platform-based field experiment in which 97,696 U.S. university-educated individuals were given the opportunity to join a tech-related product development activity. Individuals were randomly assigned to treatments emphasizing either competitive or collaborative interactions with other participants. We find that (1) in non-STEM fields, the competition treatment leads to a 27% drop in participation for females in comparison to males. However, in our main finding, (2) in STEM fields, we find no statistical differences in men and women’s responses to competition. The patterns are consistent with (3) men in non-STEM fields exhibiting overconfidence in their likelihood of succeeding under competition. We also find that, while participation in highest in STEM fields, (4) the ratio of female to male participation in a field is better predicted by whether the field is male- or female-dominated, than it is by whether it is a STEM field or not. We discuss theoretical interpretations and implications for organizations.