Dual delta-doped InGaP/InGaAs pseudomorphic high electron mobility transistors (pHEMTs) with various doping profile designs were adopted to investigate the relationship between the doping profile of pHEMTs and the surface phenomena. Compared to a single delta-doped pHEMT, the dual delta-doped design provided a high current density, which was suitable for low noise and high power applications [IEEE Trans. Electron Devices, 35, 879 (1988); J. Appl. Phys., 81, 3576 (1997)]. The influence of the delta-doped layer in GaAs Schottky diode parameters was studied [International Euroconference on Advanced Semiconductor Devices, pp. 391-394 (2000)]. The dual delta-doped and doped-channel InGaP/InGaAs pHEMTs were also investigated and studied [IEEE Trans. Electron Devices, 54, 1617 (2007)]. However, the lower/upper delta-doped layer doping profile and surface phenomena of InGaP/InGaAs pHEMTs are still ambiguous. In this work, the epitaxial concentration designs of lower and upper delta-doped layers were 1:3, 2: 2, and 3:1 (unit: 10(12) cm(-2)) for dual delta-doped InGaP/InGaAs pHEMTs, respectively. The concentration profile of the lower and upper delta-doped layers can be adjusted to realize optimal InGaP/InGaAs low noise and high linearity pHEMT. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3121731] All rights reserved.