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In this brief, we report a new observation on the abnormal gate-leakage current and associated physical mechanisms in packaged gallium arsenide (GaAs)-based n-channel pseudomorphic high electron mobility transistors (PHEMTs) with a gate length L=0.2 μm. Abnormal positive and negative humps in the gate current (IG), as a function of the gate voltage, have been investigated at room temperature. Qualitative models for the positive and negative humps in the experimental IG are proposed, combining physical mechanisms of thermionic emission, impact ionization, real-space-transfer (RST), and resonant tunneling through the alignment of quantized states in the InGaAs channel and the δ-doped AlGaAs donor layer. An experimental result is also provided for the anomalous IG under large-drain bias and forward-gate bias.