It is not known whether the very obscure Semer followed a trade. He was, however, qualified to act as an auditor, in which capacity he and Richard Sutton heard an account made at Cambridge on 12 Jan. 1422, between a fellow burgess, John Knapton*, on the one hand and a London fishmonger, John Trunche, on the other. Later that decade, Knapton pursued a suit at Westminster against Trunche, claiming that the audit had revealed that the latter owed him just over 60s.
In 1426, 1428 and 1435 the MP was considered, but not pricked, for jury service at the gaol delivery sessions held in Cambridge.
