Thermal-mechanical characteristics and outgassing efficiency of integrated in-plane outgassing channels (IPOCs) at Al2O3-intermediated InP (die)-to-Si (wafer) bonding interface is investigated. The IPOCs are introduced and investigated via both multi-physics simulation and experimental demonstration. Thermal stress simulation indicates that Al2O3 bonding layer efficiently mitigates the stress as observed at top InP surface, compared to that of conventional SiO2 intermediate layer. By introducing IPOCs, the thermal stress decreases with increasing IPOC spacing-to-width (S/W) ratio. Experimentally, high quality InP/Al2O3/Si direct bonding is firstly demonstrated. Seamless bonding interface is observed, along with reasonable bond shear strength of 2.57 MPa and minimal residual stress in the transferred InP layer. Efficiency of the IPOCs is then evaluated by comparing interfacial void densities of InP bonded on dimension-varied-IPOC-patterned Si. A significant void density reduction up to two orders of magnitude is observed, with a decreasing S/W ratio. An optimal S/W ratio of 2.5 is therefore proposed to compromise between the thermal stress degradation (~10%) and outgassing efficiency improvement (~90% void density suppression). This work is thus significant as it could provide guidelines to establish high quality hybrid-integrated optoelectronic devices for Si photonic applications.