We report on the drain-current (Id) Deep-level transient s-pectroscopy (DLTS) spectra of Si-implanted metal-semiconductor field effect transistors (MESFETs) with strong or weak Id low-frequency oscillations (LFOs) under the condition of high drain voltages (3 V-7 V). We found no distinguishing features directly related to the Id-LFO in these spectra having large peaks characteristic of the DLTS spectrum. These results imply that deep centers in the MESFET channel layer are not the direct origin of the Id-LFO.