The primary resemblance between the two is the irrational, paranoid fear that each caused. The mere suggestion that one was a witch at Salem was enough to arouse suspicions, in fact it was the accusations of a few girls who hoped to avoid punishment for their own misdeeds that led to to the entire witch hysteria. In the U.S., particularly during the Red Scare, anyone whose ideas were not mainstream was subject to suspicion, and accusations alone were sufficient to condemn one. In both instances, many innocent lives were destroyed; and in both instances the paranoia ended with the discrediting of the accusers. In Salem. the girls who started the hysteria later began writhing and accused a woman in Ipswich, a nearby village of being a witch. They were ignored. Senator Joseph McCarthy, who was widely responsible for the Red Scare, was censured by the Senate and died from alcoholism as a broken man. Finally, it should be noted that both were considered an assault on Christianity. Those accused of witchcraft were believed to have had "carnal relations" with the devil. Since Communism was atheistic, those who were accused were considered "godless."
The primary difference is that the Salem trials were at least partially based on religious principles, even though the trials were conducted by civil authorities. Salem was an intensely religious community; in fact the name itself is derived from "Jerusalem." Those accused were offered pardons if they would recant and publicly confess and renounce their misdeeds before the congregation. Those accused of communist affiliation were persecuted in a purely political environment and were not given any opportunity for recantation. A very small percentage of those accused of communist affiliation may very well have truly been communists, at least nominally; although many innocent people were implicated. No one in Salem was truly a witch. Finally, no one was put to death simply for being a communist. (Julius and Ethyl Rosenberg were put to death, but for espionage, not communist affiliation, although this may have been a factor in determining their guilt.) A number of people were hanged in Salem for no other offense than that of being a witch, and one man was crushed to death because he refused to condemn his wife.