Electrical measurements were made onn+GaAs‐(Al,Ga)As‐n−GaAs andp+GaAs‐(Al,Ga)As‐p−GaAs capacitors. Current conduction is due to thermionic emission at low bias voltages and high temperatures. At low temperatures and high fields Fowler‐Nordheim tunneling contributes to the conduction process. An invertedn‐type capacitor analogous to an inverted modulation doped structure shows electrical characteristics comparable to the ‘‘normal’’ structure grown under optimized conditions. Conduction‐ and valence‐band discontinuities were calculated from measurements of thermionic emission barrier heights as a function of Al mole fraction in the (Al,Ga)As. A conduction‐band discontinuity of 65% of the total band‐gap discontinuity between GaAs and (Al,Ga)As, independent of Al mole fraction, was deduced. A classical theory for the capacitance voltage characteristics ofp+GaAs‐(Al,Ga)As‐p−GaAs structures is presented.