A series of optical transitions between higher conduction subbands and higher heavy‐hole subbands have been observed between 77 K and room temperature in photocurrent spectra ofp‐i‐nphotodiodes including 5‐nm‐wide InGaAs/InAlAs multi‐quantum wells. The quadratic dependence of the transition energy on the heavy‐hole quantum number,l=1,2 and 3, has been clarified for each conduction‐electron quantum number,n=1 and 2. This experiment evidences the applicability of a particle‐in‐a‐box model to the energy level determination. The carrier effective masses in InGaAs wells and the related band discontinuities were analyzed. ©1995 American Institute of Physics.