The Somerville Board of Aldermen Thursday approved a $20,000 pay raise for the position of mayor.

The raise brings the mayor's salary from $125,000 to $145,000 a year.

The move was expected and came after the aldermen, on Oct. 25, approved pay raises for all non-union city employees, impacting about 150 positions in city government.

The raise came after a September study, commissioned by the city and conducted by the Collins Center for Public Management at UMass Boston, recommended it.

The study compared municipal chief executive salaries among other cities in the Boston area. The mayor of Boston, for instance, makes $175,000 a year, according to the study. The town manager of Arlington makes $159,000 a year, and the town administrator of Brookline makes $164,612 a year. Medford's mayor makes $124,705, Malden's makes $105,900 and Newton's makes $125,000. The city manager of Cambridge makes a whopping $327,091, the study says.

Meanwhile, the aldermen did not approve a raise for themselves. Based on proceedings from Thursday's meeting, it appears many aldermen did not think it would be appropriate to give themselves a raise until the city reaches a contract resolution with the Somerville Municipal Employees Association, which hasn't had a new contract since 2006.

A raise for the position of alderman would have bumped the salary from $24,999 to $25,750 a year.