NMOS drain bulk capacitance refers to the capacitance between the drain terminal and the bulk (substrate) of an NMOS transistor, impacting its switching characteristics and overall performance. And is denoted by Cdb,n. NMOS Drain Bulk Capacitance is usually measured using the Femtofarad for Capacitance. Note that the value of NMOS Drain Bulk Capacitance is always positive.