A programmable read-only memory comprises a memory cell or a plurality of such cells arranged as an array. Each memory cell comprises a transistor, such as a MOS TFT. An electronic switch allows the control electrode, such as the gate, to be substantially electrically isolated during a programming mode so that the gate is electrically floating during this mode. During the programming mode, a programming voltage is supplied across the main conductive path of the transistor, such as across the source-drain channel. The programming voltage is sufficiently large to fuse the main conduction path when the control electrode of the transistor is floating but is insufficient to fuse the main conduction path when the control electrode is not floating and is connected to a suitable defined voltage. The transistor therefore performs functions of memory cell selection while simultaneously acting as the fusible element and the arrangement requires fewer transistors which are capable of operating atthe programming current required for fusing. The memory may therefore occupy a reduced area.