Is there better SQL statement than this ?

It takes too long time to execute the following SQL statement ?

Is there better SQL statement than this ?

I didn't make any Indexes on two tables yet.

Please give me the hints.         

        select pmc.oid from productModelParam pmp, productModelCategory pmc
	where pmc.oid = pmp.oid
	and pmc.categoryValue = '3E965F2E-F64E-9ECE-1B3872409AC42428'
	and pmp.paramValue = 'TH'
	
	intersect 
	
	select pmc.oid from productModelParam pmp, productModelCategory pmc
	where pmc.oid = pmp.oid
	and pmc.categoryValue = '3E965F2E-F64E-9ECE-1B3872409AC42428'
	and pmp.paramValue = '50Vdc'
	  
	intersect 
	
	select pmc.oid from productModelParam pmp, productModelCategory pmc
	where pmc.oid = pmp.oid
	and pmc.categoryValue = '3E965F2E-F64E-9ECE-1B3872409AC42428'
	and pmp.paramValue = '0603'