This study investigates the factorial structure of a five-item questionnaire for student ratings of teaching (SRT) at a university setting. It features factor analyses of three large samples of data from a large Midwestern public university in the USA. Students completed the questionnaire at the end of courses. There were three campuses at the university, and thus three data sets in the study including an evaluation of a total of 27,693 courses with responses from a total of 1,087,652 students. An exploratory factor analysis with maximum likelihood extraction and varimax rotation was conducted to explore the factorial structure of the three data sets separately. The results indicated that there was only one factor explaining 80.99%, 77.18% and 84.94% of the variance in the Campus 1, 2 and 3 data sets, respectively. Thus, our results suggested that the data set in each campus was primarily unifactor. That the five-item SRT measure is unifactor across the courses in each of the campuses is a robust finding. Calculation of the Cronbach's alpha coefficient of the questionnaire indicated that the questionnaire had high internal consistency reliability (i.e. alpha = .94, alpha = .92 and alpha = .95) for Campus 1, 2 and 3, respectively.