WNX–Schottky diodes on semiconductor–insulator–semiconductor‐liken‐GaAs/undoped‐AlGaAs/n‐GaAs heterostructures have been fabricated at various annealing temperatures. The barrier characteristics are evaluated and compared with those of WNX–n‐GaAs Schottky contacts. At lower annealing temperatures the metal–insulator–semiconductor (MIS) like diodes exhibit superior barrier heights. However, at higher annealing temperatures (TA≥800 °C), both the MIS and WNX–n‐GaAs Schottky diodes almost have equivalent barrier heights. The ideality factors of the MIS like diodes are worse over the whole temperature range. Thicker undoped AlGaAs layers result in increased barrier heights at lower annealing temperatures (TA≤800 °C).