In 1965, the U.S. Mint discontinued issuing both Proof and Mint sets. However, as an alternative, the Mint began offering what are known as Special Mint Sets. The coins in these sets had a special finish that was most akin to the Satin Proofs of 1936 -- far better than the finish on a regular Mint State coin, but not nearly as brilliant and reflective as the finish on the Proof coins of 1937 to 1964. Collectors purchased over 2.6 million 1965 sets, but only because they had no alternative. This amount was far below the number of 1964 Proof Sets sold (3.95 million) and the total of all 1964 Proof and Mint Sets sold (4.96 million), thus the Mint took a serious hit to its revenue stream. The Mint issued Special Mint Sets in 1965, 1966, and 1967, and each year saw a declining mintage. In 1968, the Mint began offering regular Proof and Mint Sets. Collector enthusiasm returned and the mintages returned to their pre-Special Mint Set levels.
1965 Special Mint Set Half Dollar are plentiful and they are usually nice. The most common certified grade is SP66. The highest grade is SP68, which is quite scarce.
Cameo examples represent about a fourth of the total population. Deep Cameo examples are extremely scarce -- on average, only one out of every ninety 1965 Special Mint Set Half Dollars will be a Deep Cameo.