In this work, we demonstrated a low current collapse normally on Al₂O₃/AlGaN/GaN MIS-HEMT with in situ H-radical surface treatment on AlGaN. The in situ atomic pretreatment was performed in a specially designed chamber prior to the thermal ALD-Al₂O₃ deposition, which improved the Al₂O₃/AlGaN interface with ${\mathrm{D}}_{\mathrm{i}\mathrm{t}}$ of ~2 × 10¹² cm⁻² eV⁻¹, and thus effectively reduced the current collapse and the dynamic ${\mathrm{R}}_{\mathrm{o}\mathrm{n}}$ degradation. The devices showed good electrical performance with low ${\mathrm{V}}_{\mathrm{t}\mathrm{h}}$ hysteresis and peak trans-conductance of 107 mS/mm. Additionally, when the devices operated under 25 °C pulse-mode stress measurement with ${\mathrm{V}}_{\mathrm{D}\mathrm{S},\mathrm{Q}}$ = 40 V (period of 1 ms, pulse width of 1 $\mathsf{\mu }$s), the dynamic ${\mathrm{R}}_{\mathrm{o}\mathrm{n}}$ increase of ~14.1% was achieved.