A series of GaAs/In0.25Ga0.75As/GaAs pseudomorphic high electron mobility transistors (HEMTs) was grown by low‐pressure metalorganic chemical vapor deposition. The respective influences of δ‐doping time and spacer thickness on the two‐dimensional electron gas concentrations and the mobilities were studied. The maximum mobilities, μ=5600 and 22 000 cm2/V s at 300 and 77 K, respectively, appeared at a spacer thickness of 100 Å with a δ‐doping time of 0.2 min. A δ‐doped GaAs/In0.25Ga0.75As/GaAs pseudomorphic HEMT with the above parameters was fabricated. This device revealed high saturation current density of 350 mA/mm, transconductance of 95 mS/mm, and broad maximum transconductance region of 2.5 V with geometry of 2×100 μm2at room temperature. In addition, very high breakdown voltage (26 V) and low leakage current (≤2 μA at −26 V) were achieved.