A hole concentration greater than 1020cm−3in GaAs has been achieved using a liquid CCl4source for carbon in a low‐pressure organometallic vapor phase epitaxy system. The resistivity and hole mobility measured at 300 K for a heavily carbon‐doped (1.2×1020cm−3) Hall sample made from a thin (180 nm) epitaxial layer were 8.0×10−4&OHgr; cm and 65 cm2/V s, respectively. Carbon‐doped samples with excellent surface morphology were achieved using a V/III ratio of 22, and growth pressure and temperature of 80 Torr and 600 °C, respectively. A novel photoluminescence technique, based on band‐gap shrinkage of heavily dopedp+‐GaAs, has been shown to be useful for nondestructive measurement of the hole concentration in submicrometer layers.