There has been a sustained interest in student perceptions about STEM fields and their choice of careers over the past few decades. Research has shown that there is a decline in students pursuing STEM careers, and this has raised global concern. Despite these issues, no unistructural, broad, parsimonious and unambiguous quantitative instrument exists to probe student career aspirations. This paper highlights the background, extension and validation of an instrument, derived from a previous science-focussed high-quality instrument that allows student career aspirations to be quantitatively characterised. Participants were 1221 undergraduate students, 1003 of whom were judged to have provided good data, from 18 tertiary institutions in the USA and Canada. The resultant instrument is a reliable 20-question survey representing five clearly demarcated domains: Science, Technology, Engineering, Mathematics and Education. Each scale possesses high reliability (Cronbach's alpha > 0.95), and high construct validity as determined by comparisons with their stated choices of career.