His father worked for the Board of First Fruits and it is believed that he received his training from his father and in 1823-4 was taken into partnership with his father to the board under the auspices of the treasurer,
William Magee. Until Magee's death in 1831, the Semples produced at least 25 churches. Although their work is attributed to "Semple & Son", the "more idiosyncratic series of churches" dating from 1825 and 1831 are believed to be Semple junior's work. They lost their appointment to the Board of First Fruits to
Frederick Darley. After the deaths of his father and Magee, the quality of Semple's work declined. Semple then became engineer to the Pipe Water Establishment until he was dismissed in 1842. He designed Carysfort Royal School at Macreddin and made additions to
Carlow and
Wexford jails. He was declared bankrupt in 1849, and lost his Regency villas at Seaview Terrace and
Belgrave Square. After this, he lived with his brother, James, a barrister until James' death in 1869. He moved in with his eldest son, John George (died 1900) at 6 Ontario Terrace,
Rathmines in 1876. ==Selection of Works==