We provide a formula for F -thresholds of a Thom-Sebastiani type polynomial over a perfect field of prime characteristic. This result extends the formula for the F -pure threshold of a diagonal hypersurface. We also compute the first test ideal of Thom-Sebastiani type polynomials. Finally, we apply our result to find hypersurfaces where the log canonical thresholds equals the F -pure thresholds for infinitely many prime numbers.Theorem A (see Theorem 3.4). Let K be a perfect field of prime characteristic p. Let R 1 = K[x 1 , . . . , x n ] and R 2 = K[y 1 , . . . , y m ] with maximal homogeneous ideals m 1 = (x 1 , . . . , x n ) and