Okay, bear with me because I am also learning Spanish but this is my understanding: Spanish-speakers generally don't use "Estoy hambre," only "Tengo hambre." "Hambre" is a noun. So, if you were to say "Estoy [I am] hambre" that would be almost like saying, "I am SO malnourished that I have turned into hunger itself." ¡Qué dramático! If you wanted to use "estoy," you could use "hambriento," to change the noun into an adjective. But, I don't think anyone says it that way. "Tengo hambre" means, literally, "I have hunger." That is just the way people say it.

Tengo hambre o Estoy hambriento. La forma más común (al menos en la zona donde vivo) es decir: TENGO HAMBRE

"Estoy hambre" makes no sense in spanish, I share with you the rule for the use of ser/estar General "Ser" Rule Ser is used to classify and identify permanent or lasting attributes. If the general rule isn´t specific enough for you, think of the acronym DOCTOR, which stands for Description, Occupation, Characteristic, Time, Origin, and Relationship. General Estar Rule Estar is used to indicate temporary states and locations. If the general rule doesn´t suffice, think of the acronym PLACE, which stands for Position, Location, Action, Condition, and Emotion. Here is a link with mor info about it http://www.spanishdict.com/answers/100040/ser-vs.-estar#.Vjeo0n4vfZ4 Buana suerte con el español :) Saludos