We report drain-current (Id) deep level transient spectroscopy (DLTS) spectra and liquid-encapsulated-Czochralski-technique (LEC) GaAs crystal effect on low-frequency-oscillation (LFO) of wide gate (400-μm) Si-implanted GaAs metal- semiconductor field- effect- transistors (MESFETs). In the range of this experiment we could not find distinguishing DLTS peaks surely to be linked with Id-LFO of the MESFETs. Stoichiometric-melt growth LEC-boules showed relatively large Id-LFO phenomena. As-rich-melt growth LEC-boules showed tolerance to Id-LFO. We conclude that Id-LFO is not directly linked to deep centers themselves but interaction between deep centers and potential profiles and electrons. Stability of potential profile or band profile depends on “pinning’ center, which affects Fermi-level or quasi-Fermi-level stability. ‘Pinning’ center such as EL2s of ‘LEC GaAs crystals” is essential.