ARLINGTON, Mass. — A special election is being held to fill the state Senate seat left vacant by the death of Kenneth Donnelly.

Democrat Cindy Friedman, who served as Donnelly’s chief of staff, won a three-way Democratic primary last month in the district that includes Arlington, Billerica, Burlington, Woburn and much of Lexington.

No Republicans ran in the primary, so the only other candidate on Tuesday’s special election ballot will be Ian Jackson from the Green Rainbow party.

Donnelly, a retired firefighter, represented the district from 2009 until his death in April from a brain tumor.