We report the first demonstration of metal‐semiconductor field‐effect transistors (MESFETs) made from GaAs structures grown with an alkylarsine source, tertiarybutylarsine (t‐BuAsH2). MESFET fabrication was performed in parallel ont‐BuAsH2and arsine‐grown wafers to enable direct comparison of device characteristics. The GaAsn+‐nMESFETs made witht‐BuAsH2exhibited excellent saturation and pinch‐off characteristics, and diode performance comparable to arsine‐grown devices. Although the peak transconductancegmwas lower than that achieved with the arsine sample, the form of thegmversus gate voltage curves for thet‐BuAsH2‐grown devices were characteristic of well‐behaved GaAs MESFETs. These initial results demonstrate the capability oft‐BuAsH2for growing electronic device structures having good carrier transport properties and effective isolation layers.