Doris Roberts died from a massive stroke ... according to her death certificate.
TMZ obtained a copy of the doc, filed in L.A. County Court -- and it reveals the "Everybody Loves Raymond" star had been suffering from hypertension for years.
The immediate cause of death though ... was a "large hemorrhagic cerebrovascular accident" ... the medical term for a stroke.
Doris died at home last month. She was 90 years old.