A single witness for the prosecution testified in the latest session of the start-and-stop trial in the Crimean capital, Simferopol, while two other prosecution witnesses failed to appear, RFE/RL reported.
Semena faces up to five years in prison if convicted by Russia, which has jailed several Crimeans who have opposed or criticized Moscow's 2014 seizure of the Black Sea peninsula from Ukraine.
The charge against 66-year-old Semena stems from an article he wrote for RFE/RL's Krym.Realii (Crimea Realities) website in 2015. The Kremlin-installed authorities in Crimea have charged that the article called for the violation of Russia's territorial integrity.
Semena contends that he is innocent, saying that he has the right to openly express his opinions and that Crimea's status was and remains in dispute.
Semena told RFE/RL on April 17 that the charge against him is "not legal but political." He said that while the Russian Constitution guarantees the freedom of expression, "in fact people are being prosecuted for that."
The witness who appeared in court on Aprill 18, Yulia Kozhemyakina, testified that she had seen the article that led to the charges against Semena. She had been enlisted by investigators to be present as a witness when they were examining the article on a web page.
But a lawyer for Semena, Emil Kurbedinov, said that Kozhemyakina was unable to answer some of the questions from the defense and did not appear to fully understand the witness statement that she had signed.
"When we asked, 'Do you know what this technical term means?' the witness said [she] did not," Kurbedinov said.
Two other prosecution witness failed to show up for the court session.
The United States, the European Union, the Organization for Security and Cooperation in Europe (OSCE), and international media watchdogs have expressed concern about Semena's prosecution.
Read alsoOSCE condemns deterioration of media freedom, journalist safety in occupied UkraineActivists say his trial is part of a persistent Russian clampdown on independent media and dissent in Crimea since Moscow's takeover.
Russia seized control of the Ukrainian region in March 2014 after sending in troops, engineering a takeover of the administration, and staging a referendum that has been denounced as illegal by Kyiv, the United States, and a total of 100 UN member countries.
In March, the European Parliament called on Moscow to free more than 30 Ukrainian citizens who are in prison or face other conditions of restricted freedom in Russia, Crimea, and parts of eastern Ukraine that are controlled by Russia-backed separatists.
The European Parliament has urged Russia to allow Semena and the others listed to travel freely. Semena is barred from leaving Crimea and must seek permission from the Russian-imposed authorities to travel outside Simferopol.
In September, RFE/RL President Thomas Kent described the case against Semena as "part of a concerted effort by Russian and Russian-backed authorities to obstruct RFE/RL's journalistic mission to provide an independent press to residents of Crimea."
Semena's trial began on March 20, but was swiftly adjourned until April 3 and was then adjourned again until April 18. The next trial date, May 3, is the UN-designated World Press Freedom Day.