The present disclosure provides a microcontroller unit and its fabrication method. The microcontroller unit includes a logic control substrate, and also includes at least one memory die and at least one non-memory die, which are disposed on the logic control substrate. The logic control substrate includes a semiconductor device layer and an interconnection dielectric layer. A central processing unit and at least one logic controller are formed in the semiconductor device layer. All memory dies are disposed on the interconnection dielectric layer side by side or stacked one over another, and the at least one memory die is electrically connected to the central processing unit through a corresponding electrical interconnection structure in the interconnection dielectric layer. All non-memory dies are disposed on the interconnection dielectric layer side by side or stacked one over another and are electrically connected to corresponding logic controllers through corresponding electrical interconnection structures in the interconnection dielectric layer.