Samuel Monroe Jr. -- famous for his work in "Menace II Society" -- died of respiratory failure and meningitis ... with pneumonia also playing a role.

TMZ obtained the actor's death certificate ... and it states Samuel's cause of death was respiratory failure and a coccidioidal meningitis infection.

Sepsis pneumonia is listed as a contributing factor ... and the doc states he's been buried at a Los Angeles cemetery.

As we reported ... Joyce Patton -- Samuel's mom -- told us he died last month. Sam was hospitalized with a severe case of meningitis and MRSA pneumonia in April. On Facebook, she asked fans to pray for his family, especially his 3 kids.

In addition to 'M2S,' Samuel Monroe Jr. also appeared in "Tales From The Hood," "Set It Off," "Don't Be a Menace to South Central While Drinking Your Juice in the Hood" and "The Player's Club."

Shawna Stewart -- who told us she was Samuel's wife -- had his power of attorney and was in charge of his finances at the time of his death. She's listed on the death certificate as well.

He was 52.