Surface states on n-type Al0.24Ga0.76As were studied using capacitance deep-level transient spectroscopy (DLTS). Two types of hole-like traps (labeled as H1 and H2 in this work) were observed in a Al0.24Ga0.76As/In(0.22)Ga(0.78)AS pseudomorphic high-electron-mobility transistor with a multifinger gate. But, no hole-like traps were observed in the fat field-effect transistor (FATFET) having a negligible ratio of the ungated surface to the total area between the source and the drain. This provides evidence that the hole-like trap peaks in the DLTS spectra originated from surface states at the ungated Al(0.24)Ga(0.76)AS regions exposed between gate and source/drain electrodes. The activation energies for both surface states were determined to be 0.50 +/-0.03 and 0.81 +/-0.01 eV. The comparison of activation energies of the two surface states with the Schottky barrier height 0.66 +/-0.01 eV suggests that H1 and H2 are deeply related to the Fermi energy pinning levels at the Al0.24Ga0.76As surface.