A new ultra-high-frequency transistor having a maximum frequency of oscillation of over 1 kMc/s and a gain-bandwidth product of about 800 Mc/s is described. It also has extremely low-leakage and usable d.c. current gain down to 1 μA and is seen to offer special advantages for application at extremely low current levels in logic circuitry. At the same time, owing mainly to the low collector capacitance of 0·6 pF (excluding the case), it is capable of operating at switching speeds of from 100 kc/s to 1 Mc/s at collector currents of 1–10 μA, respectively. Diode-transistor logic, in general, and a new form using backward diodes, in particular, are seen to offer advantages in conservation of fan-in and fan-out at a given current level. This is especially important as the level is reduced. The latter form offers in addition a saving in number of components required. D.C. conditions necessary to assure operation are considered, and it is seen that the circuits are feasible if the proper balance between diode and transistor voltages may be achieved. If not, then compensated circuits, using extra diodes either in series or as clamping elements, enable operation. The desirable features of a device which would satisfy the requirements are illustrated by the characteristic curve of an experimental silicon backward diode. Performance is further demonstrated by a working four-stage shift register designed around a basic building block operating at 10 μA per transistor stage. The shift register operates satisfactorily at 200 kc/s from −40 to +100°C. It draws a total of about 360 μA. A computer using 10,000 such stages would draw a total current of about 100 mA at a power level of 300 mW.