1,209,543. Resistors; semiconductor devices. INTERNATIONAL BUSINESS MACHINES CORP. 8 Feb., 1968 [15 Feb., 1967], No. 6339/68. Headings H1K and HIS A resistor comprises semi-conductor material doped with both donor and acceptor-type shallow-level impurities, the total impurity concentration being greater than 8 Î 10<SP>18</SP> atoms/cm.<SP>3</SP> and the relative concentration of the two types of dopants being such as to create between 1À7 x 10<SP>18</SP> and 1À3 Î 10<SP>19 </SP>free carriers/ cm.<SP>3</SP>. With these concentrations the effect of impurity scattering on the carrier mobility is enhanced relative to that of lattice scattering so that, over the operating temperature range, the resistor has a zero or negative temperature coefficient. Preferably the donor concentration exceeds the acceptor concentration, the ratio between the two being between 1:1 and 3:1. In one embodiment (Fig. 1a) the resistor is constructed by depositing a masking layer 13 of SiO 2 on a phosphorus-doped silicon base 11. Arsenic and boron are then diffused, either together or in two separate diffusion processes, into region 15 through an opening in the masking layer, and, finally, a masking layer 17, metal contacts 19 and a further masking layer 21 are deposited in succession.