The present disclosure is drawn to a thermal inkjet printhead stack with an amorphous metal resistor, including an insulated substrate and a resistor applied to the insulated substrate. The resistor can include from 5 atomic % to 90 atomic % of a metalloid of carbon, silicon, or boron; and from 5 atomic % to 90 atomic % each of a first and second metal of titanium, vanadium, chromium, cobalt, nickel, zirconium, niobium, molybdenum, rhodium, palladium, hafnium, tantalum, tungsten, iridium, or platinum, where the second metal is different than the first metal. The metalloid, the first metal, and the second metal can account for at least 70 atomic % of the amorphous thin metal film.