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 delta-doping time and spacer thickness on the two-dimensional electron gas concentrations and the mobilities were studied. The maximum mobilities, mu=5600 and 22 000 cm2/V s at 300 and 77 K, respectively, appeared at a spacer thickness of 100 angstrom with a delta-doping time of 0.2 min. A delta-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 x 100 mum2 at room temperature. In addition, very high breakdown voltage (26 V) and low leakage current (<2 muA at -26 V) were achieved.