the surface but remains separated therefrom by a surface layer which is sufficiently thin to transmit electrons generated due to breakdown due to the highly doped p type region 53 the pn junction has within the openings 48 a low breakdown voltage so that the electron emission takes place practically solely in the regions 43 at the area of the openings 48 furthermore the arrangement can be provided with an electrode 46 with which the generated beam 8 may be deflected or modulated if desired the semiconductor body has an opening 42 within the annular pattern 47 for passing electrons generated by the cathode 20 for contacting the n type zone 51 a contact hole 55 is provided in the oxide layer 45 for a contact metallization 56 while on the lower side the substrate 50 can be connected via a highly doped p type zone 57 and a contact metallization 58 within the openings 48 a monolayer 59 of for example caesium is formed on the surface 44 in order to reduce the work function for the electrons for a further description of the structure the operation and the method of manufacturing the semiconductor device shown in fig2 and 3 reference may be made to the netherlands patent application no 7905470 the advantages of the subdivision of the emission pattern 47 into several regions 43 are described more fully in the non prepublished netherlands patent application no 8403538 the electrons for the electron bombardment on the cathode 20 can also be obtained by means of a thermionic cathode fig4.