Nonlinearity of the piezoresistance effects inp‐ andn‐type silicon was measured at room temperature for three surface impurity concentrations and for three crystallographic orientations <100≳, <110≳, and <1¯1¯2≳. Piezoresistance coefficients up to third order in stress were obtained experimentally. Uniaxial stresses up to about 174 MPa were applied with currents flowing either parallel (longitudinal configuration) or perpendicular (transverse configuration) to them. A complete set of nine independent second‐order tensor components was determined. The second‐order piezoresistance coefficients in various configurations of uniaxial stress, current, and crystallographic orientation were calculated by the sixth rank tensor transformation. The nonlinear piezoresistance effect inn‐type silicon was discussed with the many‐valley model.