  In the current paper we study extremal semilattices with respect to their
equational properties. In the class $\mathbf{S}_n$ of all semilattices of order
$n$ we find semilattices which have maximal (minimal) number of consistent
equations. Moreover, we find a semilattice in $\mathbf{S}_n$ with maximal sum
of numbers of solutions of equations.
