The 127-item Science, Technology, Engineering, Mathematics (STEM) Interest Complexity Inventory and 15-item General STEM Interests Scale, each of which were previously developed to assess interests toward increasingly complex tasks, were shortened to 37-item and 12-item measures. Item response theory analyses employed on the data of 930 students in STEM majors indicated items with higher discrimination parameters and equivalent functioning across genders. The short form (SF) supported a four-factor structure of interests toward interacting with numerical data, symbolic data, spatial data, and STEM-related ideas. Concurrent criterion-related validation was supported with relevant vocational fit criteria. Hierarchical regression analysis revealed that STEM interest complexity added incremental variance over achievement motivation and test anxiety in predicting fit. Measurement invariance was demonstrated across samples from Turkey and the United States. The STEM Interest Complexity Inventory SF is a valid measure of vocational interests for research at the college level. Validities with high school and working samples are yet to be demonstrated.