The company, founded by Hammy and Janet McMillan in 1960, currently comprises North West Castle in Stranraer, Cally Palace Hotel and Golf Course in Gatehouse of Fleet and Fernhill Hotel in Portpatrick.
Hammy and Janet are now retired and son Douglas is the managing director, while daughters Fay and Gail work in the business along with son-in-law Graham Cowan and daughter-in-law Susy McMillan.
Most of the 13 grandchildren have also worked in the business at one time, but have all chosen different career paths, so a decision has been made to seek new owners.
Graham & Sibbald have been chosen as agents for the sale, with all 150 jobs to be automatically transferred over to the new employer under TUPE regulations.
Fay said: “Having come through a global pandemic and emerged stronger and more resilient, the family believes now is the right time to set the wheels in motion.
"The hotels were trading well before Covid, and have been trading exceptionally well since re-opening.
"There is no rush. The family will take as long as is necessary to find the safest hands for their business and will continue to work hard for the future of the company.
"We hope our staff and our loyal customers will continue to support the hotels in their usual way.”