In this work we study the generalized Weierstrass semigroup H(P m ) at an m-tuple P m = (P 1 , . . . , P m ) of rational points on certain curves admitting a plane model of the form fIn particular, we compute the generating set Γ(P m ) of H(P m ) and, as a consequence, we explicit a basis for Riemann-Roch spaces of divisors with support in {P 1 , . . . , P m } on these curves, generalizing results of Maharaj, Matthews, and Pirsic in [14].