CREATE TABLE table_50566 ("Tournament" TEXT, "Surface" TEXT, "Week" TEXT, "Winner and score" TEXT, "Finalist" TEXT, "Semifinalists" TEXT)

Which Surface has Semifinalists of wally masur malivai washington?
SELECT "Surface" FROM table_50566 WHERE "Semifinalists" = 'wally masur malivai washington'
SELECT "Surface" FROM "table_50566" WHERE "Semifinalists" = 'wally masur malivai washington'