forming a p-well and an n-well in a substrate;

forming a stack of interleaving first semiconductor material layers and second semiconductor material layers over the p-well and the n-well, the first semiconductor material layers having a first thickness and the second semiconductor material layers having a second thickness that is different than the first thickness;

annealing the stack of interleaving semiconductor layers;

patterning the stack to form fin-shaped structures including a first fin-shaped structure over the n-well and a second fin-shaped structure over the p-well;

performing an etching process to remove the second semiconductor material layers from the first and second fin-shaped structures, wherein the first semiconductor material layers have a different thickness within each of the first and second fin-shaped structures after the etching process; and

forming a metal gate over the first and second fin-shaped structures.