This is a continuation to the paper [Li15a] in which a problem of minimizing normalized volumes over Q-Gorenstein klt singularities was proposed. Here we consider its relation with K-semistability, which is an important concept in the study of Kähler-Einstein metrics on Fano varieties. In particular, we prove that for a Q-Fano variety V , the K-semistability of (V, −K V ) is equivalent to the condition that the normalized volume is minimized at the canonical valuation ord V among all C * -invariant valuations on the cone associated to any positive Cartier multiple of −K V . In this case, it's shown that ord V is the unique minimizer among all C * -invariant quasi-monomial valuations. These results allow us to give characterizations of K-semistability by using equivariant volume minimization, and also by using inequalities involving divisorial valuations over V .Definition 2.5 ([Ber15, Fuj15b]).1. Let (V, L)/C 1 be a normal semi-test configuration of (V, r −1 K −1 V ) and (V,L)/P 1 be its natural compactification. Let D (V,L) be the Qdivisor on V satisfying the following conditions: L) is a Z-divisor corresponding to the divisorial sheafL(r −1 KV /P 1 ).
The Ding invariantDing invariant Ding(V, L) of (V, L)/C is defined as:3. V is called Ding semistable if Ding(V, L) ≥ 0 for any normal test configuration (V, L)/C of (V, −r −1 K V ).