There are 13 14-letter words that start with 'sem'.
| semasiological | semiautomatics | 
| semiautonomous | semicentennial | 
| semicommercial | semiconducting | 
| semiconductors | semidarknesses | 
| semiofficially | semiologically | 
| semiporcelains | semiretirement | 
| sempiternities | |
Note: These 13 14-letter words that start with 'sem' are found from the USA & Canada version of the tournament Scrabble word list.
Also see words start with semi, sema, seme, semp, semb, semo.
4-letter words start with 'sem' (2)