Allowed transitions between then=1, 2, and 3 subbands of the conduction and valence bands of a multiple quantum well heterostructure of GaAs‐Al0.6Ga0.4As are seen in spontaneous emission under high excitations. The observed peaks agree very well with the calculated locations of the peaks when the finite depth of the potential well and the nonparabolicity of the conduction band are taken into account. The same basic features are seen under cw or picosecond pulse excitation and at room temperature, 77 K, or 4.2 K.