2D semiconductor devices have been studied due to their unique potential in architecture and properties. As one of the unique devices approaches, 2D hetero-stack channel field-effect transistors (FETs) have recently been reported, but homo-stack FETs are rare to find. Here, MoSe2/MoSe2 homo-stack transistors are rather fabricated for study. Unlike the equivalently-thick single MoSe2 FET, homo-stack FETs show n-type memory behavior that originates from stack interface-induced traps. Particularly, when their stack interfaces are engineered by surface oxidation of bottom MoSe2, more stable nonvolatile memory behavior turns out. Short-term ultraviolet ozone (UVO)-induced oxidation only results in n-type memory, but 15 min-long oxidation surprisingly enables both n- and p-type nonvolatile memory behavior due to nm-thin MoOx embedded between upper and lower MoSe2. Furthermore, by alternating gate voltage pulse to the 15 min-long UVO-treated FETs, channel polarity conversion appears reversible in a small gate voltage (VGS) sweep range, which means that the channel type of a transistor can be reversibly modulated via stack interface engineering. It is believed that homo-stack interface engineering must be one of the approaches to maximize the potential of 2D devices.