Semipostal stamps are issued for fund raising purpose. Generally, those type of stamps have two denominations separated by a plus sign, but in many cases the only denomination shown is for the postage rate, and the postal customer simply pays the higher price when purchasing the stamps. The extra money stamp-buyers pay goes to the charity described on the stamps. Semipostals became widespread in European countries at the beginning of the 20th century.

Here are some semipostal stamps for sale on eBay.