To cite SemiMarkov in publications use:

Agnieszka Krol, Philippe Saint-Pierre (2015). SemiMarkov: An R Package for Parametric Estimation in Multi-State Semi-Markov Models. Journal of Statistical Software, 66(6), 1-16. URL http://www.jstatsoft.org/v66/i06/.

Corresponding BibTeX entry:

  @Article{,
    title = {{SemiMarkov}: An {R} Package for Parametric Estimation in
      Multi-State Semi-Markov Models},
    author = {Agnieszka Kr\'{o}l and Philippe Saint-Pierre},
    journal = {Journal of Statistical Software},
    year = {2015},
    volume = {66},
    number = {6},
    pages = {1--16},
    url = {http://www.jstatsoft.org/v66/i06/},
  }