Thermoelectric　materials　are　typically　highly　degenerate　semiconductors,　which　require　high　carrier　concentration.　However,　the　efficiency　of　conventional　doping　by　replacing　host　atoms　with　alien　ones　is　restricted　by　solubility　limit,　and,　more　unfavorably,　such　a　doping　method　is　likely　to　cause　strong　charge-carrier　scattering　at　ambient　temperature,　leading　to　deteriorated　electrical　performance.　Here,　an　unconventional　doping　strategy　is　proposed,　where　a　small　trace　of　alien　atoms　is　used　to　stabilize　cation　vacancies　in　Cu3SbSe4 by　compositing　with　CuAlSe2,　in　which　the　cation　vacancies　rather　than　the　alien　atoms　provide　a　high　density　of　holes.　Consequently,　the　hole　concentration　enlarges　by　six times　but　the　carrier　mobility　is　well　maintained.　As　a　result,　a　record-high　average　power　factor　of　19 µW cm−1 K−2 in　the　temperature　range　of　300–723 K　is　attained.　Finally,　with　further　reduced　lattice　thermal　conductivity,　a　peak　zT　value　of　1.4 and　a　record-high　average　zT　value　of　0.72 are　achieved　within　the　diamond-like　compounds.　This　new　doping　strategy　not　only　can　be　applied　for　boosting　the　average　power　factor　for　thermoelectrics,　but　more　generally　can　be　used　to　maintain　carrier　mobility　for　a　variety　of　semiconductors　that　need　high　carrier　concentration.　©　2022　Wiley-VCH　GmbH.