I found a Semos Costakis (note the spelling) in the 1920 California census, age 27, born in Greece, single, general laborer, as a boarder in a private home in Vallejo, CA. He was boarding with Aurelia Silva, a Mexican widow, and her children Luke, Amelia, Henry and Ignacio. This Semos immigrated in 1912, and was not naturalized as a citizen at the time of this census.