A programmable read only memory includes a matrix of semi-fusible link memory cells, each including a semi-fusible link having an intact impedance and a blown impedance; a bit line voltage supply switching circuit for applying a current to at least one selected bit line; a word line address decoder for selecting a word line; and a program control logic circuit for blowing the semi-fusible links in the memory cells identified by the intersection of the selected word and bit lines; a method is disclosed of testing programmed and unprogrammed read only memory.