over the surface or the wafer and the oxide layer 23 then the wafer is subjected to a rapid thermal annealing treatment which causes the silicon in contact with the cobalt to form a cobalt disilicide contact member 26 the member 26 is in good ohmic contact with the underlying tasi 2 rods and also forms a rectifying contact with the silicon of the matrix the unreacted cobalt is removed in a suitable etching solution which does not attack the cobalt disilicide contact member the device at this stage is illustrated in fig4 next the wafer is coated with a layer of a photoresist material 28 and openings are formed in the photoresist layer 28 and the oxide layer 25 to expose the surface areas 17 and 18 for the source and drain regions fig5 the wafer is treated by ion implanting a suitable doping material into the exposed source and drain regions 30 and 31 with the photoresist layer 28 protecting the remainder of the wafer specifically phosphorous is implanted in order to produce heavily doped low resistivity n type regions 30 and 31 in the high resistivity n type silicon matrix after the ion implantation procedure the photoresist material is removed and the wafer is subjected to a rapid thermal annealing treatment in order to activate the ion implanted phorphorus as illustrated in fig5 the heavily doped source and drain regions 30 and 31 do not extend to the uppermost portions of the rods 12 which are recessed below the surface and polycrystalline silicon 21 lies interposed between the rods and the source and drain regions the wafer is then treated in accordance with known procedures to produce ohmic contact members to the source and drain regions a layer of titanium tungsten alloy ti w.