Fabrication of a P-stabilized GaP(001)-(2 x 1) surface with t-butylphosphine (TBP) at very low pressure (5 x 10(-7) Torr) has been studied by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), reflection high-energy electron diffraction (RHEED), and Auger electron spectroscopy (AES). A (3 x 2) structure is found at small area when a GaP(001)(2 x 4) surface was exposed to TBP (70-240 L) at 623 K. Increasing the amount of TBP leads to formation of a disorder surface. The (2 x I) surface structure appeared by exposing the (2 x 4) surface to about 540 L-TBP. It is found that the (2 x 1)structure is reconstructed into the (2 x 4) by annealing the (2 x 1)surface at 673 K in an ultrahigh vacuum.