This paper proposes an algorithm to construct an X-clock tree with double via insertion that connects several voltage islands for power minimization. We first construct the X-clock tree for each voltage island and make double via insertion for this tree to improve yield and reliability. Then we combine these X-clock trees based on a well-defined connection with inserted level-shifters to reduce power. The delay effect due to total number of vias is also accounted. Experimental results show that X-clock trees based on multi-voltage islands have 22.46% and 5.41% less than that of single voltage island in terms of power and delay, respectively.