The hidden parameters aren't visible in the v$parameter view and this is why the "show parameter" doesn't work. Try this query, works for me. You have to be logged as sys.
Code:select a.ksppinm name, b.ksppstvl value, b.ksppstdf deflt, decode (a.ksppity, 1, 'boolean', 2, 'string', 3, 'number', 4, 'file', a.ksppity) type, a.ksppdesc description from sys.x$ksppi a, sys.x$ksppcv b where a.indx = b.indx and a.ksppinm = '¶meter_name' /