Who were the semifinalists when the runner-up was Pat Du Pré?
CREATE TABLE "table1_29302781_12" (
  "week_of" text,
  "tournament" text,
  "champion" text,
  "runner_up" text,
  "semifinalists" text,
  "quarterfinalists" text
);
SELECT "semifinalists" FROM "table1_29302781_12" WHERE "runner_up"='Pat Du Pré';