Abstract: A meet semilattice with a partial join operation satisfying some axioms is a JP-semilattice. In this paper we study the modular and distributive JP-semilattices. We give several characterizations of modular and distributive JP-semilattices. We also prove the Separation Theorem and its extension for minimal prime ideal of distributive JP-semilattices. JP-congruences, have also been studied.