Nigel Davies faced embarrassment last month after forgetting to renew his nursing registration but it did not affect his managerial position and his resignation this week was a shock to colleagues.
The exodus from the trust's eight-member board began when chairman Colin Maclean took early retirement in December. His deputy, Irene Inskip, announced her departure a month ago.
Chief medical officer Jonathan Fielden left last month for a post at London's University College Hospital. Former Reading community relations chief Rajinder Sohpal finished his term of office in March, and fellow non-executive member Ken Hydon, a former Vodafone finance director, has retired.
Reading East MP Rob Wilson said: "I'm in close touch with the hospital and ensuring that the needs of patients and the quality of treatment they receive is at the forefront for everybody in the Trust. Clearly the management turbulence is unhelpful to the process."