1. A multi-bit-per-cell three-dimensional read-only memory (3D-OTP MB ), comprising: a semiconductor substrate including transistors thereon; an OTP array stacked above said semiconductor substrate, said OTP array comprising a plurality of OTP cells including a first unprogrammed dummy OTP cell, second and third programmed dummy OTP cells, each of said OTP cells comprising an antifuse layer, wherein said second and third programmed dummy OTP cells have different states; a first dummy bit line associated with said first unprogrammed dummy OTP cell; a second dummy bit line associated with said second programmed dummy OTP cell; a third dummy bit line associated with said third programmed dummy OTP cell; a plurality of contact vias coupling said OTP cells to said semiconductor substrate; a differential amplifier with an input disposed on said semiconductor substrate, wherein said input is coupled with said first and second dummy bit lines during a first measurement, and said input is coupled with said second and third dummy bit lines during a second measurement; wherein said OTP cells have more than two states, the OTP cell in different states being programmed by different programming currents.