optical power is formed by radiation with a wavelength of 254 nm with which a photovoltage of approximately u2212 0 5 v can be obtained by applying said voltage to the control gate during erasure a threshold voltage of approximately 1 3 v was obtained during erasure in a specific embodiment an initial threshold voltage being approximately 1 1 v whereas a threshold voltage of approximately 1 8 v was obtained during erasure if this voltage was not applied to the control gate the decoder circuit 4 controls the word lines 2 as is diagrammatically shown in fig1 usually each word line is connected to the output of a cmos transistor pair as a result of this each photodiode is connected via the word line not only to one or several control gates but also coupled to semiconductor zones which form a pn junction in the semiconductor body this is diagrammatically shown in fig3 the output stage comprises an n channel transistor 20 and a p channel transistor 21 the transistors are shown diagrammatically only and it should be noted that certain components which form standard features of transistors such as source drain extensions or spacers on the side walls of the gates have not been shown for simplicity 39 sake the n channel transistor 20 comprises n type source and drain zones 22 and 23 formed in the p type surface region 5 and a gate 24 the p channel.